1. Field of the Disclosure
Embodiments disclosed herein relate generally to the processing of a C5 olefin stream, such as may be formed from a C5 hydrocarbon cut from a cracking process, for conversion of the C5 olefins to butenes via isomerization and metathesis.
2. Background
It is known to convert pentenes to propylene via metathesis. For example, when linear pentenes are fed to a conventional metathesis reactor, having a catalyst bed including a mixture of isomerization and metathesis catalysts, the following reactions may occur:(a) 1-pentene→2-pentene  (Isomerization);(b) 2-pentene+ethylene→1-butene+propylene  (Metathesis);(c) 1-butene→2-butene  (Isomerization);(d) 2-butene+ethylene→2 propylene  (Metathesis).1-Pentene is isomerized to 2-pentene. The metathesis reaction of 1-pentene with ethylene is non-productive (products are same as reactants). The overall linear C5 olefin reaction for the production of propylene can thus be shown as:1 mol linear pentene+2 mol ethylene→3 mol propylene.
Butadiene demand, however, is increasing. Butadiene is a versatile raw material used in the production of a wide variety of synthetic rubbers, polymer resins and chemical intermediates. The largest uses for butadiene are the production of styrene butadiene rubber and polybutadiene rubber, which are used mainly in tire products. Butadiene is also one of the components used in the manufacture of acrylonitrile-butadiene-styrene, styrene-butadiene copolymer latex, styrene-butadiene block copolymers and nitrile rubbers. There is a growing demand for butadiene caused by the growth in tire demand as well as reduced natural rubber production.
The major source of butadiene is as a byproduct in the steam cracking of naphtha and gas oil to make ethylene and propylene. Steam cracking is a process by which hydrocarbon molecules are exposed to very hot steam, causing them to break apart into smaller molecules. Separation of butadiene from the other products of the steam cracking process typically includes the use of extractive distillation. Other potential sources for the production of butadiene include converting feed stocks comprising butene and butane compounds and mixtures thereof to butadiene.